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CONCUBINAGE. 255 CONCUSSION OF THE BRAIN. They not only upheld thoroughly the principle of mon'ogauiy, but they fettered marriage itself with iiKuiy burdensome forms. Hence arose the prac- tice of a free unmarried man enterinj,' into a less strict relation with a single woman — a sort of ]iernianent cohabitation. The oUsiJring of such a connection, called 'uaturar children, had not the rights of legitimate children, but they were recog- nized bj- the father. Augustus, with a view to promote regular marriages and check the growing licentiousness, enacted a comjjrehcnsive nuirriage- law (Lex Julia), which discouraged conculiinage, restricting it to women of low rank or those who had lost their station. Christianity reijuired the complete sanctity of marriage and taught that concubinage was sinful, and we find the Synod of Toledo legislating against it as far back as A.D. 400. The ancient laws of the Ger- n'.ans recognized, along with regular marriage, an informal connection of the sexes. In the Middle Ages a similar connection became cus- tomary, called a 'left-handed,' or morganatic marriage. See JIakki.ge, and consult the au- thorities there referred to. CONCURRENCE (ML. concurrentia, con- currence, from coiicurrere, to run together, from com-, together + c»rrcrf, to run) and COL- LINEARITY (from Lat, com-, together + Ztneo, line ) . If several lines have a point in common they are said to be concurrent. The common point is called the focus or vertex of the pencil of lines. If several points lie on one straight line they are said to be collinear. The line is called the base of the range of points. That portion of geonjetry concerned with concurrent lines and collinear points is called the theory of concur- rence and collinearity. Some of its fundamental propositions are : If a transversal intersects the sides of a tri- angle ABC in the points X, Y, Z, the segments of the sides of the triangle are connected by the relation (AZ:ZB)- (BX:XC) • (CY: YA) = - 1. Conversely, if the points be so taken that the rela- tion holds, then the three points are collinear. (This relation is known as Menelaus's theorem.) If the three lines AO, BO, CO drawn from the vertices of the triangle ABC are concurrent in and meet the opposite sides in X, Y, Z, then BX • CYAZ = — CXAY-BZ, and conversely (Ceva's theorem ) . If three lines perpendicular to the sides of a triangle ABC at X. Y. Z are concurrent, then BX= — XC= + CY- — YA= -f AZ= — ZB= = 0. Conversely, if this relation holds, the per- pendicvilars are concurrent. If the lines joining the vertices of two tri- angles are concurrent, their corresponding sides intersect in three collinear points. (This proposi- tion, known as Desargues's theorem, is true for any rectilinear figvires. ) The opposite pairs of sides of a hexagon in- scribed in a conic intersect in three collinear points ( Pascal's theorem ) , The lines joining the opposite vertices of a hexagon circumscribed about a conic are con- current ( Brianehon's theorem ) . The polars of a range of points with respect to a circle (q.v.) are concurrent, and conversely. If from any point on a circle perpendicvilars are drawn to the sides of an inscribed triangle, their feet are collinear. (The base of this range is called Simson's line.) From these and other similar theorems, many properties of elementary geometry follow at once; as, the altitudes of a triangle are concurrent, the medians of a triangle are concurrent, etc. The theorems of Pascal and Brianchon lead to numer- ous theorems in modern geometry. Consult: Cre- mona, Elements of Projective Geometry, trans, by Leudesdorf (Oxford, 1885) ; Casey, Seqvel to Euclid (Dublin, 1888) ; Beman and Smith, New Plane and tioUd Ueometry (Boston, 1900) ; Mc- Clelland, Geometry of the Circle (New York, IStU). CONCURRENT JURISDICTION. The jurisdiction that exists where two or more courts possess the equal and coordinate right of taking cognizance of a single cause. Thus in the United States, a justice's court and a city court may often take cogiiizance of the same matter; or a court of common pleas and a superior court may do the same. In criminal cases it is an estab- lished rule that when one court has brought an ofTender before it, the court having concurrent jurisdiction is thereby debarred from taking cognizance of the case. In civil trials it is the privilege of the person appealing to the law — that is, in most cases, the plaintitf — to choose !>efore ^vhich of the two coordinate courts he wishes to bring the matter. The phrase concur- rent jurisdiction is used in opposition to priva- tive, or exclusive, jurisdiction, i.e. where only one court has the right of hearing and determin- ing the matter at issue. In the political system of the United States, with its Federal courts exercising jurisdiction over the same persons as are subject to a local State jurisdiction, the occurrence of cases of con- current jurisdiction is very common. Where it exists, a decision of a State court may, in a proper case, be taken up to the Supreme Court of the United States for review. See Court; JUEISOICTIOK. CONCUSSION FUSE. See Fuse. CONCUSSION OF THE BRAIN (Lat. con- cussio, shock, from concutcrc, to shake together, from com-, together -^- ^Hfl/or, to .shake). The name given to a group of symptoms which result from injuries to the head, but are not due to fracture or to perceptible laceration of vessels or brain substance. The condition has been widely discussed and extensively studied by many means of experimentation, but authorities still disagree as to whether it is due to laceration of minute blood-vessels, to altered vibratory changes in the molecules of the brain-cells, or to a change in the disposition of the cerebro-spinal fluid. At present, almost all surgeons deny that concussion of itself is fatal, and autopsies show almost in- varialily some apparent lesion of vessels or brain substance in those fatal cases which have simu- lated concussion, but which were really instances of contusion or laceration. The symptoms vary in mild and severe cases. In the former, when the patient is 'stunned' by a fall or a blow on the head, there is dizziness, disturbances of vision and noises in the ears, loss of strength, so that the patient falls, the face is pale and covered with a cold perspiration, the respiration is shal- low, the pulse feeble and often slower than normal. In graver cases these symptoms become intensified, or the most extreme symptoms may develop instantly. There is complete unconscious- ness, the body is cold and relaxed, the pupils widely dilated and unresponsive to light, the